Fair Value Measurements - Nonrecurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Carrying Amount
Financial Instruments
Long-term debt, excluding current portion	$ 8,974	$ 6,731
Fair Value
Financial Instruments
Long-term debt, excluding current portion	$ 10,260	$ 7,203

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